The thing about the Fae rules is that they're about giving the protagonists a chance. Learn these rules, and you're safe if you abide by them.

They could be more of an honour system thing, they can break the rules, but if they do, they forfeit the protections afforded by those rules, which is bad when those rules are the means by which you can maintain your power (and/or magically binding oaths of fealty) So you could have lesser fae that are less rulebound but also less powerful, while the scariest people in the Fae are also the most rulebound, but of course employ lesser fae to get around said rules, (with perhaps the occasional 'for this particularly scary being, all bets are off.')

So you could have different kingdoms with different rules, you're safe in one court of you abide by their rules...but some of their rules conflict with an enemy court who are bound by different rules, some can be bent, some can be broken, others are deeply ingrained by tradition or a magically binding treaty sworn 500 years ago...